What is a stem cell
unspecialised cell from the embryo, feutus, or adult
under certain conditions, has self-renewal capability by reproducing itself for long periods of time, in adult stem cells, for the life of the organism
can differentiate whereby unspecialised cells give rise to specialised cells that make up tissues and organs of the body
has large nuclear to cytoplasmic ratio
has ability to replenish its population and generate cells that travel down various differentiation pathways
Unique features of stem cell
- unspecialised
* no tissue-specific structures to allow it to carry out specialised functions
* can differentiate to give rise to specialised cells - capable of dividing and self-renewal for long periods of time
* stem cells able to replicate many times through mitosis and give rise to unspecialised cells capable of long-term self-renewal via mitosis
* to be able to maintain a constant pool of unspecialised cells - Able to give rise to specialised cells
* differentiation triggered by internal and external signals - potency
* range of cell types stem cell can give rise to
* determined by the number of pathways it can take in its subsequent development through differentiation
* reflects the differential potential of a stem cell
What is totipotency
- master cells that can give rise to all cell types of an organism
- consists only of zygotic stem cells
- exits as the zygote and the first few cells produced by the rapid division of stem cells through mitosis to form the morula
- can differentiate into any cell type in the adult body and any cell of the extra-embryonic membranes
- occur at the early stages of embryonic development before blastocyst stage
formed within up to the first 5 days of fertilisation
What is pluripotency
- formed 5-7 days after fertilisation
- derived from totipotent stem cells
- able to differentiate into cell types from the 3 germ layers
1. mesoderm
2. endoderm
3. ectoderm - do not have the potential to differentiate into cells of the extra-embyronic membrane
- embryonic stem cells is a type
- found only in inner cell mass of early human embryo
- fetal tissue destined to be part of the gonads
What is multipotency
- formed 7 days after fertilisation
- derived from pluripotent stem cells
- able to differentiate into different cell types within a specific type of tissue
- more specialised than totipotent and pluripotent stem cells
- example is adult stem cells
- usually found in adult animals
What are committed stem cells
- derived from pluripotent stem cells
- multipotent and unipotent stem cells
- more specialised than pluripotent stem cells and are destined to produce a specific group of cells
- can give rise to more specifically committed cells or progenitor cells
What are progenitor cells
- intermediate cell types generated by stem cells before achieving their fully differentiated state
- in fetal or adult tissues are slightly differentiated and divide and give rise to differentiated cells
- show some evidence of differentiation although the process is not complete until fully differentiated cell has been formed
- committed to a limited number of differentiation pathways
- more limited in developmental pathways than multipotent stem cells
What is symmetric division
stem cell divides via mitosis into 2 genetically identical daughter stem cell with same potency and differential potential as the parental stem cell
What is asymmetric division
due to localisation of regulatory molecule or differentiated segregation of cell membrane proteins, stem cel divides via mitosis into one daughter stem cell genetically identical to parental cell and one progenitor cell that differentiates to form specialised cell
Significance of proginetor cells/asymmetric division
preserves population of undifferentiated cells while giving rise to a steady stream of differentiated cells
Importance of stem cells
potencies determined by surroundings and once committed usually do not change their committment
important for maintaining cell populations that last for long periods of time and needs renewal
Differences between embryonic stem cells and adult stem cells
refer to page 13 of notes
Sources of embyronic cells in the human body
- inner cell mass of blastocyst
- precursors to gonads of aborted fetuses
Properties of embryonic stem cells
- can undergo an unlimited number of symmetrical divisions without differentiating(long-term self-renewal)
- exhibit and maintain a stable, full, normal complement of chromosomes
- able to give rise to any cell type derived from the 3 primary germ layers of an embryo
- able to develop into all fetal tissue during development
- colonogenic: can give rise to a large colony of genetically identical cells that have the same properties as the original cell
- easier to obtain pure and cultivate in large numbers
What does ESC become in a developing embryo
inner cell mass initially a two layered disc then 3rd layer forms
- ectoderm is the layer nearest the amniotic cavity
- endoderm is the layer nearest the blastocyst cavity
- mesoderm forms in the middle of the 2 layers
the 3 layers form the gastrula or primordial embryo
Activities of adult stem cells
- undifferentiated cells found among differentiated cells in a tissue or organ
- able to renew itself and differentiate to yield the major specialised type in the tissue or organ
- rare: dispersed in tissues throughout the body + number of adult stem cells in body at any one time low, hard to identify and obtain
- adult stem cell types do not grown well in culture as they lose their distinctive cellular properties
- main roles:
1. maintenance and repair of specialised cells of the tissue they are found in
2. replace cells that die because of injury or disease
origin of adult stem cells in mature tissues is unknown
Properties of adult stem cells
- capable of long-term self-renewal
- able to give rise to fully differentiated cells that have mature phenotype, fully integrated into tissue, and have specialised functions appropriate of the tissue
- cologenic and is able to to undergo mitotic division to give rise to a colony of genetically identical cells that can give rise to, and differentiate to form specialised cell types appropriate of the tissue they reside in
Types of cells in the blood plasma and their adult stem cell
red blood cells: erythocytes
white blood cells: leukocytes
platelets
formed from hematopoietic stem cells(HSC) located in the bone marrow, a multipotent/adult stem cell
What is hematopoiesis
formation of blood
Information on of hematopoietic stem cells
- derived from the mesoderm in an embryo and colonise a number of definitive blood-forming sites
- primary role is to replace blood cells
- all blood cells originate from hematopoietic stem cells in the bone barrow
- HSCs capable of self-renewal and are precursors of progenitor cells that committ to one of the hematopoietic lineages
- hematoesis is a complete developmental system in itself whereby a single cell differentiates to give many cell types
Role of hematopoietic stem cells
- differentiate into specialised blood cells to replace worn out blood cells
- capable of long-term self-renewal to ensure continuous supply of blood stem cells througout lifetime of organism
- what the different lineages gives rise to
What are the 3 lineages of hematopoietic stem cells
Lymphoid lineage:
* produces a type of white blood cells called lymphocytes, including B lymphocytes and T lymphocytes
* B lymphocytes:
1. come from the bone barrow, function to produce antibodies and fight against infections
2. develop in the bone marrow
* T lymphocytes:
1. attack virus-infected cells, cancer cells, foreign cells
2. produce substances that regulate the immune response
* Both cells undergo further terminal differentiation after encounter with antigen
Myeloid lineage:
* gives rise to the rest of the red blood cells which are all derived from the bone marrow
* includes eosinophils, neutrophils, basophils(known as granulocytes, polymorphonuclear leukocytes) monocytes, mast cells
* mobile units of the immune system that function to:
1. defend against pathogen infections via phagocytosis
2. identification and destruction of cancer cells that arise from within the body
3. clean up crew, phagocytize debris from injured or dead cells during wound healing or tissue repair
Erythroid lineage:
* gives rise to erythrocytes: transport of gases in the blood
* the megakaryocytes that gives rise to blood platelets: blood clotting functions
How is differentiation of hematopoietic stem cells regulated
regulated by the niche that they inhabit, which includes stromal cells of the bone marrow
regulated by secreted signal proteins and stromal cells which provides external signals in the form of hematopoietic growth factors and cytokines
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LIPIDS 🍔15
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CARBOHYDRATES 🍬🌱29
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PROTEINS 💪47
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ENZYMES 📈28
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EUKARYOTIC CELL STRUCTURE AND FUNCTION 🧫28
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CELL MEMBRANE AND TRANSPORT35
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DNA STRUCTURE AND REPLICATION30
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Eukaryotic Gene Expression54
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Organisation of Eukaryotic genome24
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Control of gene expression14
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Gene and Chromosomal mutations11
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Molecular Techniques11
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Bioethics0
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CELL SIGNALLING38
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CELL AND NUCLEAR DIVISION33
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CANCER 😵21
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Stem cells23
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PHOTOSYNTHESIS10
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CELLULAR RESPIRATION0
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BACTERIA0
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INHERITANCE59
